Traffic-recording equipment for telephone systems



June19,1928. 1,674,411

J. E. OSTLINE TRAFFIC RECORDING EQUIPMENT FOR TELEPHONE SYSTEMS 7 e 6 4 3 2 9 a 7 6 4 3 2 mvs FHA/rm; X 5 4 5 2 I I (av/vi) June 19, 1928.. 1,674,411

- J. E. OSTLINE TRAFFIC RECORDING EQUIPMENT FOR TELEPHONE SYSTEMS ril 18, 1924 s Sheets-Sheet 2 K K2 K3 MARGINAL June 19, 1928.

J. E-. OSTLINE TRAFFIC RECORDING EQUIPMENT FOR TELEPHONE SYSTEMS .3 Sheets-Sheet 3 Original Filed April 18, 1924 QLF Patentted Junel 9 l928. K

.UNITED STATES PATENT OFFICE.

JOHN E. osrLmE, or LIVERPOOL, ENGLAND, nssrefion, BY mEsNE nssmmmar AUTOMATIC ELECTRIC 1y OF CHICAGO,

rumors, A conromrron or DELAWARE.

'rnn rrrc-nnconnme EQUIPMENT FOR TELEPHONE SYSTEMS.

Application filed April 18, 1824, Serial No. 707,419. Renewed January 9, 1928.

The present invention relates in general to traffic recording equipment for telephone systems, and is particularly concerned with the provision o appropriate equipment at a central point -for recording "traflic over trunk groups of a multi-ofiicetelephone system.

In manual practice, in order to determine the trafiic, what is known as the peg count method, has been used to some extent. This method consists of thecounting of connect'ions set up at regular intervals, and gives a fair' idea of trafiic loads if carried out consistently. .The difiiculty in applying this method to automatic connections is the time and labor which is required in countingthe connections from either switches or repeaters.

The chief object of the present invention, therefore, is to provide traflic recording equipment which will accurately record the number of busy trunks of a group during agiven time. H

.Another object is to provide equipment for the above purpose, which may be economically manufactured, is entirely automatic in its operation, and which is very flexible in that it can be used in both automatic and manual systems.

Another object is to so design the above apparatus that the actual recording equipment can be placed in a centrally located oflice and all recording controlled thereat, thereby reducing the labor involved in taking and tabulating the observations to a minimum.

Referring now to the drawings, Figs. 1 to 3. when laid out with Fig. 2 immediately below Fig. '1, and 3 to the right of Fig. 2, show by means of the usual diagrams suflicient of the circuits and apparatus to enable the invention to -be readily understood. V

Referring to the'drawings more in detail, Figs. 1 and 2 taken together show all of the equipmentin the recording oflice. This equipment mainly consists of a register or recording apparatus R, a digit selecting switch DSS, and an ofiice selecting switc OSS.

The register Rconsists of a. three column motor driven printing type addingmachine arranged so that the usual key levers or as many of them as are'used, are operated by magnets. A machine which W1 I serve is.

the well known Burroughs, in which keys corresponding. to the different digits of a number are epressed, followed by the de- PI'BSSlOIl of the starting or printing key, whereupon the number corresponding to the depressed keys is printed on a tape. According to the circuit arrangement disclosed herein only the keys in the units and tens columns and the first five hundreds keys are used, in addition to the key for controlling 05 the printing action. As indicated on the drawing, which shows diagrammatically the magnets which operate the. keys, the five hundreds keys are used to indicate ofiicers while the tens and units keys indicate the number of connections, providin for recording a maximum of 99 connections "in anyone offive difierent offices. As an example, the number 369 appearing on the tape would indicate 69 connections in office No. 3.

The switches DSS and 055s are of the usual and well known rotary type commonly used as individual line switches. The switch DSS, however, instead of having double wipers, has two sets of single wipers set at a 180 degree angle, one set engagin its'fi'rst set of bank contacts as the other set 'disengages its last set. In this manner a fifty contact switch is obtained.

In*addition to the apparatus above described a number of relays, a number of" manually operable keys, and a cam 70 are provided. The relays are for various switching operations which will be described hereinafter. The keys comprising keys K to K are ofiice keys and are provided to enable. an attendant to disconnect the recording equipment from association with any office when desired. With these keys in normal position, traffic in all the offices is re-" corded. a record being made first of. the traffic in one office, then the next, and so on,

until all oflices have been tested, when the recording apparatus starts over again with the first office. The cam 70 is constantly rotating at the rate of one rotation per- 'minute and is eifective when the key K is inoperated position to periodically cause the release of the recording equipment and to 'cause the ofiice selecting switch OSS to move its wipers into association with the trunk extending to the next oflice in which trafiic is to be recorded.

Fig. 3 shows the countin equipment of one ofiice ,(all other ofiices eing provided with like equipment), which consists of two counting switches CS and CS'. These switches are mechanicall DSS of Fig. 1. As wil be seen from the drawing, each of these switches has access to the release conductors of fifty trunk lines making a total of one hundred trunks which may be observed in a single oflice. The pur-' poses of the various relays in this figure will be fully described hereinafter.

In order to enable the invention to beclearly understood, the operation of the system will now be described in detail.

' K a circuit is completed which includes slow releasing relay 64 1n the recording office and high resistance relay 101 in the No. 1 oifice. This circuit may be traced from grounded conductor 19, contacts of start key K, arma ture 67 and its resting cont-act, springs controlled by armature 58, winding of relay 64, wiper 72, startconductor 20, springs controlled by armature 104, and the winding of high resistance relay 101 to battery.

For the present we will consider only what takes place in office No. 1. Due to the high resistance of relay 101, relay 64 in the recording oifice does'not operate at this time. Relay 101 in oflice No. 1, however, operates and at its armature 102 completes a circuit for the motor magnet 119 of the counting switch CS. This circuit extends from grounded working contact of armature 102 and the said armature, armature 114: and its resting contact, wiper 121, resting contact of armature 116 and the said armature, armature 109 and its resting contact, armature 117 and its restingcontact, and the winding of motor magnet 119 to battery. The operation of relay 101.also completes a circuit for slow releasing relay 107. This circuit extends from battery, resistance 110,

the winding of relay 107, armature 116 and its resting contact, and the grounded wiper 121. During the time motor magnet 119 is at normal, however, relay 107 is short circuited by ground on wiper 121 being extended by way of interrupter springs 120, resting contact of armature 115 and the said armature to the resistance 110. As soon -as the motor magnet 119 operates this short the same as switch For this purpose it will be assumed that thecounting equipment shown in Fig. 3 of the the recording oflice, and at its-armature 109 opens a pointin the previously described relay deenergizes a new-circuit is completed for the motor magnet 119 which extends from the grounded multipled bank contacts 130, wiper 121, resting contact of armature 116 and the said armature, armature 109 and its resting contact, armature 117 and its resting contact, and the winding of motor magnet 119 to battery. The operation of motor magnet 119 again causes the short to be removed from slow relay 107, permitting this lay to be again energized to open the circuit of the motor magnet. This alternate operation of motor magnet 119 and slow rela 107 continues until the wipers 121-124:, inclusive, have completed a complete revolution, the wiper 122 being substituted for the wiper 121 when the switch takes its twenty-fifth step. The switch CS upon taking its forty-ninth step positions its wiper 122 on contact 131 which, instead of being connected to direct ground, supplies ground through the winding of low resistance relay 105. Motor magnet 119 operates as before and relay 105 also operates. Relay 105,- upon operating, at its armature 106 completes a circuit for the lower winding of relay 111. Relay 111 only operates its armature 114 when its lower winding alone is energized. This armature, upon operating, breaks a point in the originai operating circuit of magnet 119 and completes a shunt about the upper winding of relay 111. As soon as magnet 119 is fully operated relay 107 again operates and breaks the operating circuit of relay 105 and magnet 119. Relay 105 deenergizes thereby removing ground from the lower terminal of the upper windingof relay 111. Current now flows through both windings of relay 111 and this relay now operates its armatures 112, 113 and 115 to 117, inclusive. At armature 113 a circuit is prepared for relay 103, and at armatures 115 to 117 and their working contacts switch CS is substituted for switch CS. The deenergizatirm of magnet 119 causes the wipers of switch CS to be moved another step into their initial starting posit-ion. Upon the deenergization of relay 107, since relay 111 is now operated, a circuit is completed for motor magnet 118 of the switch CS. This circuit may be traced from battery, winding of the motor magnet 118, working contact of armature 117 and the said armature, resting contact of armature 109 and the said armature, armature 116 and its working contact, wiper 125 and its first bank con- I tact, working contact of armature 114 and takes its forty-ninth step the relay 105 again operates, this time in series with magnet 118 and, since armature 113 is in operated position, causes the operation ofrelay 103. Relay 103, upon-operating, substitutes its low resistance locking winding for the high resistance relay 101. Relay 101 .deenergizes and in so doin breaks the locking circuit of relay 111. his latter relay accordingly restores to normal. All equipmentat the No.

1 office is nowin its orlginal position with the exception of relay 103. The substitution of low wound relay 103 for relay 101 causes the current flow 1n the conductor 20 and in the relay 64 (Fig. 2) to be materially increased for a purpose which will subse quently be pointed out.

As. previously pointed out,

the conductors extending from the bank contacts traversed J the connections extending to the operatlng by wipers 123, 124, 127 and 128 extend to release trunk conductors of the trunk group upon which tratfic is to .be recorded, or, if manual trunks are being observed, to conductors of such trunks adapted to be grounded when taken for use.'

Since, as previously stated, each of the fifty bank contacts of switch CS and OS are connected to the release-trunk conductor of a different trunk, it follows that Wipers 123 and 124 in travelling over their respective bank contacts, upon engaging grounded or busy release trunks, cause impulses to be transmitted back over conductor 132, resting cont-act of armature 112 and the said armature, armature 108 and its working contact to count conductor 129 extending to the recording equipment at the centralized oflice. wiper 73 (Fig. 2), and the winding of pulsing relay 51 to battery. As previously explained, the various conductors of the switch OS are substituted for those of S when the relay 111 is operated, and therefore the wipers 127 and 128 in :rotating andupon engaging grounded contacts cause impulses to be sent out overconductor 133, workingcontact of armature 112 and the said armature, over the previously described circuit to the pulsing relay 51. J We will now turn our attention to what takes place in the recording oflice responsive to the impulses transmitted over conductor 129 to pulsing relay51. -Each time the pulsmg relay 51 operates a circuit is completed ,18,i.e.,itwil for the digit selecting switch DSS, from the grounded start conductor 19, springs of battery, winding of motor magnet l0, con- 1 ductor 38; interrupter springs 23, conductor 24, wiper 15, conductor 25, conductor 37,

springs controlled by armature 55, winding DSS, upon com of relay 52, conductor 39, resting contact of armature 68 and the said armature, spiings of key K to the grounded conductor 19. Relay 52 operates, at its armature 54 closes a point in the operating circuit of switching relay 18, and locks itself up over a circuit including both its windings and its armature 55 in series. It Will be seen that since the operating circuit of relay 18 must include wiper 15 and its first contact this relay cannot become energized "uniess the wiper 15 is moved fifty steps.

he reason for the above arrangement will be quite evident after a slight study of of relay "be seen that the operation of any combination of magnets to register numbers from one re fortymine may be accommagnets of reigister R via contacts plished without the operation of relay 18, 4

but if any number greater than 49 is to be registered relay 18 must be operated. For the purpose of illustration it will be assumed that, during the operation of switches CS and CS, fifty-five busy (grounded) trunks.

are engaged and, consequently, the motor magnet 10 causes the switch DSS to take fifty-five steps. WVhen switchDSS takes its fiftieth step wiper 15 is again positioned on its first contact and since relay 52 is now in an operated condition a circuit is completed for switching relay 18. This circuit extends from battery, winding of magnet 10, interrupter. springs 23,- conductor 24, wiper 15, conductor 42, resting contact of armature 57 and the said armature, armature 54 and its workin contact, conductor 41 and the upper twin ing of relay 18 to ground. Relay 18, upon operating, locks itself up over a circuit extending from battery, lower winding of said relay, working contact and upper armature of said relay, conductor 39, resting contact of armature 68 and the said armature, conductor 29, and contacts of key K to grounded conductor 19. Relay 18 upon operating the remainder of its armatures disconnects certain of the magnets of register R, used only when digits of less than fifty are to be registered, and connects up certain of the magnets, used only when digits of fifty or over are to be registered.

It was hereinbefore pointed out that when switches CS and CS have each completed a c cle of operation that the current flow t rough relay 64 is increased by the substi tution of the low winding of relay 103 for the high winding of relay 101. Relay 64 therefore operates, at its armature 63 completes a circuit for'slow-relay 60, and at its armature applies ground potential to conductor 43. The grounding of conductor 43 causes circuits to be completed for the oflice register magnet 1 and certain of the number recording magnets of the register R. The circuit for the oilice magnet may be traced from grounded conductor 43, branch conductor 35, wiper 74 of the oflice selecting switch OSS, conductor 48, and the winding of oflice magnet 1 to battery.

Since it has been assumed that fifty-five trunks were busy in the oifice No. 1, during this particular recording period, the tens and units magnets 5 and 5, respectively, of the register R, will be the ones operated. The circuit for tens magnet 5 may be traced from the grounded conductor 43, branch conductor 31, wiper 11 now standing on itsfifth bank contact, conductor 22, armature 27 and its working contact, conductor 28' and the winding of the tens magnet 5 to battery. The circuit for the units magnet 5 may be traced from the grounded conductor 43, branch conductor 33, wiper 13, now standing on its fifth bank contact, conductor 26, and the winding of units magnet 5 to battery. As'previously pointed out, at the same time that ground was applied to conductor 43' a circuit was also completed for slow release relay 60. This latter relay, upon operating, at'its armature 62 closes a point in the operating circuit of the register control magnet X of the register R, and at its armature61 completes a circuit for relay 56. Relay 56, upon operating, at its armature 57 opens a point in the initial circuit of switching relay 18, and at its armature 58 locks itself up by way of the resting contact and armature 67 of relay 66. Relay 56 also, at its armature 59 closes a point in a restoring circuit for the switch DSS, and at springs controlled by armature 58 opens the energizing circuit of slow release relay 64 and relay 103. This latter relay, which is located in the No. 1 oflice, deenergizes, again connecting the relay 101 to the start conductor 20. Relay 64, upon restoring, at its armature 65'removes ground from conductor 43, but this in no way affects the operated armatures of magnets of the register R since these armatures are mechanically locked in operated position until registration has taken place. Relay 64, upon retracting its emur armature 63, opens the circuit of slow release relay 60, and at the back contact of the armature 63 completes a circuit for the motor start relay of the register R. This circuit may ,be traced from grounded con-' ductor 29, armature 63 and its resting contact, working contact of armature 62 and the said armature, conductor 40, and the winding of motor start relay to battery. This circuit isopened a moment later when relay 60 retracts its armatures. The construction of the register R is such that the armature of the register control magnet 2C and the armatures of the magnets are locked up when operated and are not unlocked until the motor of the register has caused the registering operation to be completed at which time the unlocking of the armature of the register control magnet takes place. It will therefore be seen that the opening of the circuit of this magnet in no way affects the registering operation. Relay 60, upon retractlng its armature 61, completes a circuit for restoring switch DSS- to normal. This circuit may be traced from grounded conductor 29, armature 61 and its resting contact, working contact of armature 59 and the said armature, conductor 37, to the multipled bank contacts associated with wi ers 15 and 16, in the present case by way 0 wiper -15, conductor 24, interrupter springs 23, and

the winding of motor magnet 10 to battery. Since this circuit includes the interrupter springs of motor magnet 10, it will be evident that this magnet will operate its armature in the manner of a buzzer and, in so doing, move wipers 11-16, inclusive, around until they are in the position shown in the drawing. In this position, since the wiper 16 is not on any of its bank contacts, and further since the wiper 15 is positioned on an ungrounded bank contact, no further opera- .tion of the switch DSS occurs until this switch is again started by the counting relay 51 in the manner previously described.

At this stage of the operation, all equipment at the recording ofiice is at normal with the exception of switching relay 18, relay 52,

. and relay 56, these relays being still held up by current supplied through armatures 67 and 68 of slow release relay 66- As soonas the time interval of one minute elapses cam 7 0 momentarily operates its spring 30, thereby momentarily completing a circuit for slow release relay 66 and motor magnet 69 in multiple. Relay 66, upon operating, at its armatures 68 and 67 breaks the previously described holding circuit of relays 18, 52'and 56, and these relays accordingly restore to normal. Relay 66 also, at its armature 67 and its working contact, applies ground to. private conductor 37 of switch DSS, as soon as relay 56 restores its armature 59, but this has no efiect at this time as this switch is already at normal. Magnet 69, upon energizing and again deenergizing", moves its wipers 71-74, inclusive, into engagement with their second bank contacts with which are associated the conductors extending to oflice No. 2 and the conductor extending to the ofiice magnet 2 of the register R. Relay 66, upon restoring, now completes a circuit for the "slow acting relay 6 1 and the relay 101 of the second ofiice to be observed. This circuit extends from the grounded conductor 29, armature 67 and'its resting contact, through springs controlled by armature 58, winding of relay 64, wiper 72, now positioned on its second contact, and the start conductor 20' to the relay 101 located in the second oflice. The operations which take place in the second ofi'ice and in the recording ofiice from now on will be similar to those hereinbefore described and therefore need not be repeated.

After a registration has been made in each I of the five oflices the wiper 71 is stepped on to the sixthpontact, and since this and the remaining contacts in the bank are grounded the switch OSS will automatically rotate until wiper 71 is a ain positioned on its first bank contact. It, in the meantime, none of the keys, K inclusive, have been operated traflic conditions in offices 1-5, inclu- 'sive, will. be again recorded at one minute. intervals in sequence as before, but if any of the keys have been operated, the correspondin bank contact associated with wiper 71 will be grounded, and when the wiper 71 reaches such bank contact registration in that oflice will be omitted.

When it is desired that registration of all offices. be discontinued the attendant restores startikey K to normal. The restoration of this key causes ground to be removed from "conductor 29, thereby opening the circuit of any of the relays 18, 52, or 56, which may be operated at this time. The restoration ofkey K also grounds conductor .37. The ground on this conductor will cause the switch DSS to restore to normal in the same manner previously described. The switch OSS has no normal position and therefore its wipers remain on the contacts associated with conductors extending to the particular oflice which is being observed at the time the start key is restored, unless the wiper 71 happens to be on one of the bank contacts not utilized, which, as will be seen, is permanentl grounded, and in this case the switch SS will automatically rotate until the wiper 71 comes into engagement with the first bank contact with which an. ob- .served oflice is associated.

. evident to those skilled in the art that, with out increasing the equipment at the recording oflice, trunk groups from twenty-five ofiices may be handled.

' In the preceding description it was as-- sumed that the start key just after the cam had operated spring 30. A brief description will now be given of'the operations which take place should the key K be operated when the cam 70 is at some other position. Under these conditions the operations take lace as previously 2 described except that, i switches CS and CS fail to have completed their cycle of operation, which may-often be the case, when spring 30 is grounded, relay 64 will not be energized and,therefore, conductor 43 will not be grounded and no partialregistration will take place. Relay 66, upon operating, at its armature 67 and its working contact extends ground via resting contact of armature 59 and the said armature to private conductor 37 to restore switch K was operated DSS to normal. When ground is removed from spring 30 magnet 69 restores and in so domg moves 1ts associated wipers 1nto conneetion with the next contact set. Relay 66,

upon retracting its armatures, connects the relay 64 in series with the relay 101 of the ofliee selected by switch OSS, and the recording equipment is now in readiness to periodically testing the busy or idlecondition of all trunks in the associated group in group of the selected 1 a definite order, and automatic means common to all the said groups for recording the number of the particular group and the number of trunks busy in such group in each instance.

2. In a telephone system, a main office,'a branch oflice, a trunk line connecting said offices, a group of trunk lines in'the branch oflice, means for making said trunk lines busy, means in the branch office for testing the idle or busy condition of said trunk lines, means atthe main office controlled by said testing means to register the number of trunks found busy, a recording device at the main ofiice for recording the number set up on said register device, and a relay as sociated with said testing means operated only when all said trunks-have been tested for causing the operation of said recording device. v

3. In a telephone system, a main ofiice. and a plurality of branch oflices, aftrunk li tending from each branchoflice to said" ain oflice, a plurality of trunks'at each branch office for use in lnter-eonnecting calling and called bubscribers lines, traflic recording equipment at the main oflice, means associated with said recording equipment auto-.

matically 0 erated to connect any branch ofiice therewith for a predetermined interval, testing apparatus at such branch ofiice for determining the number of trunks that are in use at one time, means at the main ofiice for initiating the operation of said testing apparatus, means in said testing apparatus for transmitting an impulse of current to the recordin apparatus each time a busy trunk is foun and means in said testing apparatus automatically 0 erated when all trunks associated therewiisi have been tested for causing a record to be printed at the recording ofilce.

4. In a trafiic recorder, or line testin devices, a common registering device, a testlng device selector for connecting said registering device with said testing devices successivel and a recording device controlled by sai registering device each time the same is connected to a testing device.

5. In a traiiic recorder, a plurality of trunk or line testing devices, each comprising means for testing a group of trunks or lines, a registering device, and means for connecting said registering device to said testing devices successively.

6. In a trafiic recorder, a plurality of trunk or line testing devices, each comprising means for testin a group of trunks or lines, a registering evice, means for connecting said registering device to said testing devices successively and means for automatically starting each testing device ,responsive to its being connected with registering device.

In a trafiic recorder, a plurality of trunk or line testing devices, each comprising means-for testin a group of trunks or lines, a regis'terin evice, means for connecting said registerin device to said testing devices successiv y, means for automatically starting each testing device responsive to its being connected with by said registering device, and means ineach testing device for setting said registe device.

8. In a traflic recorder, a p urality of trunk or line testing devices, each comprising means for testing a group of trunks or lines, a re istering evice, means for connecting sai registering device to said testing devices successively, means for automatically starting each testin device responsive to its being connected wit by said registering device, means in each testing device for setting said registering device, means for restoring the registerin device each time before it is cqnnected wit a difierent testing device, and a recording device controlled by said registerin device.

9. a telephone system, ups of trunk lines located in difi'erent te ephone oflices,

a plurality of trunk by saidtest equipment in each oflice for determining e busy or idle condition of the trunk lines therein, a common recording point, means for successively connecting said common recording oint with each of said testing devices, an means atsaid common recording point for ski ping any testing equipment in any of sai oflices at will.

10. In a telephone system, groups of trunk lines located in different te ephone oflices, testing equipment in each ofiice for determining the bus or idle condition of the trunk lines therein, a common recordin point, means for successively connectin said common recording point with each 0 said testing devices means at said common recording point for starting the testing equipment in said oflices when connected-with and for recording the traflic conditions of the groups of trunk lines in said oflices, and means at said common recording, point for skippin the testing .of any of said groups of tr lines in said oflices at will.

11. In a telephone system, 'oups of trunk lines located in different te ephone ofiices, testing equipment in each oflice for determining the busy or idle condition of the trimk lines therein, a plurality of supervising trunk lines connecting said oflices, respectively, with a common recording point, and means at said common recording point for starting the testing equipment in said oflices and fir recording the trailic conditions in the various grou s of said trunk lines by means of centre from said testing equiplllilgnt exercised over said supervising t 12. A traflic recorder, for use in recording the busy or idle conditions of lines in a telephone system, comprising means for automatically testing said lines, a printing device controlled w; said testing means and means fmeri 'cally repeating said test 'automati y.

13. In a telephone system, means for testing telephone lines and for automatically making each time a permanent record indicating the busy conditions of the lines tested. and means for automatically repeating said tests periodicaliliy.

14. In a tra 0 recording stem for recording traflic in group to ephone lines, means for testing each 0 said mes and for recordin the bus condition of the tested lines, an means or preventing the testing of any group or groups of lines while permittin the preceding group or groups of lines to e tested.

15. In a traific recorder for recording traflic conditions in grouped telephone lines, means for testing said groups of lines successively, and means automatically eflective between the testing of successive groups for recording the number of one of thqgroups.

16. In a traflic reco er or recording trafiic conditions in grouped telephone lines, means for testing said groups of lines successively, and means automatically effective between the testing of successive groups for recording the number of one of the groups and for recording the number of' lines that were busy in the last tested group.

17. In an apparatus for testing the condition of each of a number of conductors, means effective When'the apparatus has been started for-maintaining said apparatus in operation until all of the conductors have been tested and for then stopping the apparatus, and means for periodically restarting the apparatus.

18. In an apparatus for testing the condition of each of a number of conductors, means effective when the apparatus has been started for maintaining said apparatus'in operation until all of the conductors have been tested and for then stopping the apparatus, and means for periodically restartmg the apparatus, the interval between starting periods bein substantially greater than the testing perio i 19. In a telephone system, groups of trunk lines, means for periodically determining the I bus or idle condition of all of the trunks in eac group in a definite group and trunk oring the busy or idle condition of the trunk v lines therein, supervisory trunk lines connecting said offices respectively with a common supervisin point, and means, at said common supervising point for starting the testingequipment in said offices and for indicating the traffic condition in thevarious groups of said trunk lines by means of control from said testing equipment exercised over said supervisory trunk lines.

21. In an apparatus for testing the trafiic conditions in grouped tele hone lines, means for testing each of said ines in a definite group and line order, and means for preventing the testing of any group or groups of lines while ermitting the preceding group or'groups o lines to be tested.

In witness whereof, I hereunto subscribe my name this 27th day ofIMarch, A. D., 1924. I

JOHN E. OSTLIN 

